Manual wheelchair technology has greatly improved over the last 100 plus years such that many existing wheelchairs on the market today provide a very functional mobility device for active independent individuals with disability. One class of wheelchair, known as “ultra-lightweight” wheelchairs, are very light and enable a user to efficiently self-propel as well as to easily manipulate the wheelchair, e.g. to lift the wheelchair into a car. Many of these types of wheelchairs are engineered with a minimal number of components to keep weight down; such a design also has the added benefit of minimizing the visual impact of the wheelchair, thus focussing the attention of others to the user instead of the wheelchair.
The technology improvements that have led to ultra-lightweight and other types of wheelchairs have incremented over the years in the form of improved adjustability, stability, suspension, and weight. However, current state of the art chairs still suffer from the problem that once they are set up with a certain configuration, the user cannot easily alter the selected configuration. For example, ultra-lightweight chairs in particular do not let the user dynamically (in real-time) change their seating position without getting out of the chair to reconfigure the chair's configuration.
Users may prefer different seating positions for different tasks, and thus it is desirable to be able to easily reconfigure the seating position of the chair. For instance, it is desirable to sit much lower in an increased “dump” position (i.e. at a negative seat angle below the horizontal) in a chair when wheeling, much like tennis chairs or track chairs. When in this type of position, a user is more stable and is able to wheel more efficiently. The drawback to this position is that it can become uncomfortable over a long period of time and the user is at an even lower position, which entails all the negative issues associated with being ‘short’. On other occasions, it is desirable to be able to elevate the wheelchair seat above the normal sitting position. For example, an elevated position is useful for accessing countertops and higher shelves, sitting at similar heights to others (e.g. on bar stools), participating in certain activities like playing pool, and to more closely approximate the height of other people.
There is a class of wheelchairs known as “standing chairs” which offer a certain degree of dynamic seat height adjustment. Such chairs enable the user to adjust his or her height between a sitting position to a full standing position without getting out of the chair. However, these chairs suffer a major drawback in that they tend to be heavier than ultralight chairs as a result of incorporating the numerous mechanisms required to lift the user to a standing height. Furthermore, the complex mechanisms interfere with the seat's ability to lower to a sufficient low position that enables comfortable and efficient self propulsion.
There is another class of wheelchairs known as “tilt chairs” which offer individuals who are typically very disabled the ability to be put into a tilted position whereby their weight is shifted from primarily the buttocks to a larger area including the user's back, in order to redistributed the pressure on the skin. Typically the tilting operation is operated by an attendant due to the high level of disability of the user. Such chairs seek a very large degree of rearward tilt (approximately 45 degrees) that necessitate specific linkages and pivot positions. In one prior art approach, the seat pivot is placed several inches rearward of the seat front, and several inches below the seat. This pivot position, along with appropriate biasing mechanisms to tune the force of the lifting mechanism to individual user weights, enables very weak individuals to independently position themselves throughout the seat range. A disadvantage of this approach is that a user's knees move upwards as the seat is tilted which may prevent a user from fitting their legs under a table when tilted. Due to their specific design criteria, these chairs also may not provide positive tilt above the horizontal. As well the backrest assembly tilts with the seat which may inhibit the user from achieving efficient wheeling power when the seat is tilted below the horizontal.